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Biomedical subjects

M Kasuga

Publications and source records attributed to M Kasuga.

At least 127 records · Page 7Linked to original sources
PubMed1998

Clinical significance of serum hyaluronic acid as a fibrosis marker in chronic hepatitis C patients treated with interferon-alpha: histological evaluation by a modified histological activity index scoring system.

The aim of the present study was to investigate the histological changes effected by interferon (IFN) treatment and to evaluate the clinical significance of serum hyaluronic acid (HA) as a marker of fibrosis. Forty-nine patients with chronic hepatitis C treated with IFN-alpha were divided into three groups according to the existence of viraemia: sustained complete responders (CR), complete responders with relapse (PR) and non-responders (NR). Needle biopsy sections of the liver taken before and at the end of IFN treatment were assessed according to the modified histological activity index (HAI) scoring system. Serum fibrosis markers, including HA, were measured at needle biopsies. Biopsies of CR at the end of treatment showed a significant improvement in fibrosis and necroinflammatory scores. More significant correlation was observed between fibrosis scores and serum levels of HA before IFN treatment (r = 0.607, P < 0.0001) than those between fibrosis scores, on the one hand, and peptide of type III procollagen (PIIIP; r = 0.531, P = 0.0004) or type IV collagen 7S domain (type IV-C; r = 0.241, P = 0.1062) on the other. Moreover, serum HA levels fell significantly in patients in whom fibrosis improved (P = 0.011). This is the first paper describing the advantages of the modified HAI scoring system over others in estimating the effect of IFN-alpha; the results also indicate that serum HA can be useful in monitoring liver fibrosis in chronic hepatitis C patients treated with IFN-alpha.

Adult↗
PubMed1998

Peptic ulcers after the Hanshin-Awaji earthquake: increased incidence of bleeding gastric ulcers.

OBJECTIVE: Although physical stresses are known to induce peptic ulcers in the upper gastrointestinal tract, it remains controversial whether emotional stress can cause peptic ulcers. Therefore, we examined retrospectively the influence of the Hanshin-Awaji earthquake that occurred in Japan in January 1995 on the occurrence of peptic ulcer disease among noninjured residents. METHODS: Sixty-one hospitals, covering 70% of all endoscopy examinations performed in this area, joined the study and were divided into three areas according to the severity of the damage. A comparison was made between a group of 10,831 patients who underwent upper gastrointestinal endoscopy within 2 months after the earthquake and 16,100 who did so in the same hospitals during the corresponding period in 1994. RESULTS: In the most devastated area, in spite of a dramatic decrease in the total number of endoscopies (50.0%), patients with gastric ulcer (GU) were increased in 1995, whereas those with duodenal ulcer were decreased, resulting in a higher ratio of gastric to duodenal ulcers than in 1994 (3.07 vs 1.88). In particular, there was a marked increase in bleeding GU. The mean age of patients with GU was significantly higher in 1995 than in 1994. CONCLUSION: The Hanshin-Awaji earthquake-induced life event stress not only triggered but also exacerbated GU, particularly in the elderly.

Adult↗
PubMed1998

Requirement of atypical protein kinase clambda for insulin stimulation of glucose uptake but not for Akt activation in 3T3-L1 adipocytes.

Phosphoinositide (PI) 3-kinase contributes to a wide variety of biological actions, including insulin stimulation of glucose transport in adipocytes. Both Akt (protein kinase B), a serine-threonine kinase with a pleckstrin homology domain, and atypical isoforms of protein kinase C (PKCzeta and PKClambda) have been implicated as downstream effectors of PI 3-kinase. Endogenous or transfected PKClambda in 3T3-L1 adipocytes or CHO cells has now been shown to be activated by insulin in a manner sensitive to inhibitors of PI 3-kinase (wortmannin and a dominant negative mutant of PI 3-kinase). Overexpression of kinase-deficient mutants of PKClambda (lambdaKD or lambdaDeltaNKD), achieved with the use of adenovirus-mediated gene transfer, resulted in inhibition of insulin activation of PKClambda, indicating that these mutants exert dominant negative effects. Insulin-stimulated glucose uptake and translocation of the glucose transporter GLUT4 to the plasma membrane, but not growth hormone- or hyperosmolarity-induced glucose uptake, were inhibited by lambdaKD or lambdaDeltaNKD in a dose-dependent manner. The maximal inhibition of insulin-induced glucose uptake achieved by the dominant negative mutants of PKClambda was approximately 50 to 60%. These mutants did not inhibit insulin-induced activation of Akt. A PKClambda mutant that lacks the pseudosubstrate domain (lambdaDeltaPD) exhibited markedly increased kinase activity relative to that of the wild-type enzyme, and expression of lambdaDeltaPD in quiescent 3T3-L1 adipocytes resulted in the stimulation of glucose uptake and translocation of GLUT4 but not in the activation of Akt. Furthermore, overexpression of an Akt mutant in which the phosphorylation sites targeted by growth factors are replaced by alanine resulted in inhibition of insulin-induced activation of Akt but not of PKClambda. These results suggest that insulin-elicited signals that pass through PI 3-kinase subsequently diverge into at least two independent pathways, an Akt pathway and a PKClambda pathway, and that the latter pathway contributes, at least in part, to insulin stimulation of glucose uptake in 3T3-L1 adipocytes.

3T3 Cells↗
PubMed1998

Requirement for activation of the serine-threonine kinase Akt (protein kinase B) in insulin stimulation of protein synthesis but not of glucose transport.

A wide variety of biological activities including the major metabolic actions of insulin is regulated by phosphatidylinositol (PI) 3-kinase. However, the downstream effectors of the various signaling pathways that emanate from PI 3-kinase remain unclear. Akt (protein kinase B), a serine-threonine kinase with a pleckstrin homology domain, is thought to be one such downstream effector. A mutant Akt (Akt-AA) in which the phosphorylation sites (Thr308 and Ser473) targeted by growth factors are replaced by alanine has now been shown to lack protein kinase activity and, when overexpressed in CHO cells or 3T3-L1 adipocytes with the use of an adenovirus vector, to inhibit insulin-induced activation of endogenous Akt. Akt-AA thus acts in a dominant negative manner in intact cells. Insulin-stimulated protein synthesis, which is sensitive to wortmannin, a pharmacological inhibitor of PI 3-kinase, was abolished by overexpression of Akt-AA without an effect on amino acid transport into the cells, suggesting that Akt is required for insulin-stimulated protein synthesis. Insulin activation of p70 S6 kinase was inhibited by approximately 75% in CHO cells and approximately 30% in 3T3-L1 adipocytes, whereas insulin-induced activation of endogenous Akt was inhibited by 80 to 95%, by expression of Akt-AA. Thus, Akt activity appears to be required, at least in part, for insulin stimulation of p70 S6 kinase. However, insulin-stimulated glucose uptake in both CHO cells and 3T3-L1 adipocytes was not affected by overexpression of Akt-AA, suggesting that Akt is not required for this effect of insulin. These data indicate that Akt acts as a downstream effector in some, but not all, of the signaling pathways downstream of PI 3-kinase.

3T3 Cells↗
PubMed1998

Molecular screening of uncoupling protein 2 gene in patients with noninsulin-dependent diabetes mellitus or obesity.

Uncoupling protein 2 (UCP2), a member of the family of mitochondrial carrier proteins, has been implicated in the control of whole-body energy balance. The coding region of the human UCP2 gene has now been shown to comprise six exons, and the sequences of the exon-intron boundaries were determined. With the use of this sequence information, 25 Japanese patients with obesity and noninsulin-dependent diabetes mellitus (NIDDM) and 25 subjects with simple obesity were screened for mutations in the entire coding region of UCP2 by PCR and single-strand conformation polymorphism analysis. Two nucleotide polymorphisms resulting in Ala55 --> Val and Ala232 --> Thr substitutions were detected. With the use of PCR and restriction fragment length polymorphism analysis, the allele frequencies for each of these polymorphisms were determined in 210 Japanese patients with NIDDM, 42 obese individuals, and 218 normal control subjects. The frequency of the Val55 allele did not differ significantly among the NIDDM group (46.0%), the obesity group (48.8%), and the normal control group (48.4%). The Thr232 allele was detected in only three subjects, who were heterozygotes and in the NIDDM group (allele frequency, 0.7%). However, expression in yeast of the human wild-type UCP2 protein and UCP2 containing Thr232 revealed no difference in functional activity. These results indicate that the Ala55 --> Val and Ala232 --> Thr variants of UCP2 do not play an important role in the pathogenesis of NIDDM or obesity in the Japanese population.

Adult↗
PubMed1998

Shc phosphotyrosine-binding domain dominantly interacts with epidermal growth factor receptors and mediates Ras activation in intact cells.

The adaptor protein Shc contains a phosphotyrosine binding (PTB) domain and a Src homology 2 (SH2) domain, both of which are known to interact with phosphorylated tyrosines. We have shown previously that tyrosine 1148 of the activated epidermal growth factor (EGF) receptor is a major binding site for Shc while tyrosine 1173 is a secondary binding site in intact cells. In the present study, we investigated the interaction between the PTB and SH2 domains of Shc and the activated human EGF receptor. Mutant 52-kDa Shc with an arginine-to-lysine substitution at residue 175 in the PTB domain (Shc R175K) or 397 in the SH2 domain (Shc R397K) was coexpressed in Chinese hamster ovary cells overexpressing the wild-type or mutant EGF receptors that retained only one of the autophosphorylation sites at tyrosine 1148 (QM1148) or 1173 (QM1173). Shc R397K was coprecipitated with the QM1148 and QM1173 receptors, was tyrosine-phosphorylated, and associated with Grb2 and Sos. In contrast, coprecipitation of Shc R175K with the mutant receptors was barely detectable. In cells expressing the QM1173 receptor, Shc R175K was tyrosine-phosphorylated and associated with Grb2, while association of Sos was barely detectable. In cells expressing the QM1148 receptor, tyrosine phosphorylation of Shc R175K was markedly reduced. When both Shc R175K and 46-kDa Shc R397K were coexpressed with the mutant receptors, p46 Shc R397K was dominantly tyrosine-phosphorylated. In cells expressing the wild-type receptor, Shc R397K, but not Shc R175K, translocated to the membrane in an EGF-dependent manner. In addition, Ras activity stimulated by the immunoprecipitates of Shc R397K was significantly higher than that by the immunoprecipitates of Shc R175K. The present results indicate that tyrosine 1148 of the activated EGF receptor mainly interacts with the Shc PTB domain in intact cells. Tyrosine 1173 interacts with both the PTB and SH2 domains, although the interaction with the PTB domain is dominant. In addition, Shc bound to the activated EGF receptor via the PTB domain dominantly interacts with Grb2-Sos complex and plays a major role in the Ras-signaling pathway.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Effects of corticotropin-releasing factor on feeding and pancreatic polypeptide response in the dog.

We have previously reported that corticotropin-releasing factor (CRF) is a potent stimulator of adrenocorticotropic hormone and cortisol secretion in the dog. Therefore, in the present study, we investigated the extrahypophysiotropic actions of CRF in this species. When CRF was injected into the third cerebral ventricle, it failed to inhibit food intake significantly at doses of 1.19, 3.57, and 11.9 nmol. This is in sharp contrast with the results in rodents. At the 3.57 and 11.9 nmol doses, CRF markedly stimulated the secretion of pancreatic polypeptide (PP), a hormone under vagal control, and at the highest dose CRF increased plasma glucose levels. These results suggest species differences in the feeding response to CRF and activation of the parasympathetic nervous system in the dog.

Animals↗
PubMed1998

Gastric epithelial cells secrete a PDGF-like peptide, a potent mitogen for human gastric fibroblasts.

To investigate whether gastric epithelial cells secrete growth factors involved in stromal cell growth, we examined the effects of conditioned media obtained from gastric cancer cells on murine BALB/c 3T3 cells and primary cultured human gastric fibroblasts. Conditioned media from MKN-1 gastric cancer cells were applied to a heparin-affinity column. The fraction eluted from the column at 0.4 M NaCl stimulated DNA synthesis and phosphorylation of PDGF alpha-receptors on tyrosine in BALB/c 3T3 cells. The fraction-induced stimulation of DNA synthesis in gastric fibroblasts was more marked than in BALB/c 3T3 cells. However, the fraction failed to stimulate DNA synthesis in CHO-ER cells overexpressing EGF receptors and phosphorylation of PDGF beta-receptors on tyrosine in BALB/c 3T3 cells. Immunoblot analysis of the media confirmed that PDGF-AA-like peptides are released from gastric cancer cells, immortalized gastric epithelial cells, and primary cultured gastric epithelial cells. Anti-PDGF neutralizing antibodies produced only a partial inhibition of 0.4 M NaCl fraction-induced enhanced DNA synthesis. Thus, in addition to PDGF-AA peptide, other bioactive substance(s) are probably released from MKN-1 gastric cancer cells. Our results suggest that gastric epithelial cells secrete PDGF-AA-like peptides responsible for stromal cell growth through paracrine mechanisms.

3T3 Cells↗
PubMed1998

Role of binding proteins to IRS-1 in insulin signalling.

Insulin elicits its divergent metabolic and mitogenic effects by binding to its specific receptor, which belongs to the family of receptor tyrosine kinases. The activated insulin receptor phosphorylates the intracellular substrate IRS-1, which then binds various signalling molecules that contain SRC homology 2 domains, thereby propagating the insulin signal. Among these IRS-1-binding proteins, the Grb2-Sos complex and the protein tyrosine phosphatase SHP-2 transmit mitogenic signals through the activation of Ras, and phosphoinositide 3-kinase is implicated in the major metabolic actions of insulin. Although substantial evidence indicates the importance of IRS-1 in insulin signal transduction, the generation of IRS-1-deficient mice has revealed the existence of redundant signalling pathways.

Animals↗
PubMed1998

[The signal transduction of receptor tyrosine kinase].

Polypeptides such as growth factors, differentiation factors, and hormones are crucial components of the regulatory system that coordinates development of multicellular organisms. Many of these factors mediate their pleiotropic actions by binding to and activating cell surface receptors with an intrinsic protein tyrosine kinase activity. The receptor activation due to ligands binding are translated across the membrane barrier into activation of intracellular domain functions. All receptor tyrosine kinase are composed of three major domains; an extracellular domain connected via a single membrane-spanning domain to a cytoplasmic domain. The extracellular domain is responsible for ligand binding and transmission of the biological signal to the cytoplasmic domain, whose role is to transmit the biological signal to intracellular target proteins. The cytoplasmic domain contains, in addition to the catalytic protein tyrosine kinase, distinct regulatory sequences with tyrosine, serine, and threonine phosphorylation sites. It appears that ligand-induced activation of the kinase domain and its signaling potential are mediated by receptor oligomerization. Ligand binding and the subsequent conformational alteration of the extracellular domain induce receptor oligomerization, which stabilizes interaction between adjacent cytoplasmic domains and leads to activation of kinase function and autophosphorylation of themselves. These receptor and substrate phosphorylation create binding sites for SH2 containing signaling molecule, such as Grb2, Shc, PI3 kinase and SHP-2. Binding of SH2 domains to tyrosine-phosphorylated regions of receptors or adaptor proteins, and a number of protein, such as SH3 containing protein, cytosol protein tyrosine kinase, protein tyrosine phosphatase and serine/threonine kinase, mediate intracellular signaling cascade and play critical roles in activated receptor protein tyrosine kinase to downstream signaling pathways.

Animals↗
PubMed1997

Epidermal growth factor stimulates the tyrosine phosphorylation of SHPS-1 and association of SHPS-1 with SHP-2, a SH2 domain-containing protein tyrosine phosphatase.

SHPS-1 is a 120 kDa glycosylated receptor-like protein that contains immunoglobulin-like domains in its extracellular region and four potential tyrosine phosphorylation for SH2 domain binding sites in its cytoplasmic region. Epidermal growth factor (EGF) stimulated the rapid tyrosine phosphorylation of SHPS-1 and subsequent association of SHPS-1 with SHP-2, a protein tyrosine phosphatase containing SH2 domains, in Chinese hamster ovary cells overexpressing human EGF receptors. In the cells overexpressing SHPS-1, the tyrosine phosphorylation of SHPS-1 was more evident than that observed in parent cells. However, overexpression of SHPS-1 alone did not affect the activation of MAP kinase in response to EGF. These results suggest that SHPS-1 may be involved in the recruitment of SHP-2 from the cytosol to the plasma membrane in response to EGF.

Animals↗
PubMed1997

Regulation of eIF-4E BP1 phosphorylation by mTOR.

The proteins eIF-4E BP1 and p70 S6 kinase each undergo an insulin/mitogen-stimulated phosphorylation in situ that is partially inhibited by rapamycin. Previous work has established that the protein known as mTOR/RAFT-1/FRAP is the target through which the rapamycin.FKBP12 complex acts to dephosphorylate/deactivate the p70 S6 kinase; thus, some mTOR mutants that have lost the ability to bind to the rapamycin.FKBP12 complex in vitro can protect the p70 S6 kinase against rapamycin-induced dephosphorylation/deactivation in situ. We show herein that such mTOR mutants also protect eIF-4E BP1 against rapamycin-induced dephosphorylation, and for both p70 S6 kinase and eIF-4E BP1, such protection requires that the rapamycin-resistant mTOR variant retains an active catalytic domain. In contrast, mutants of p70 S6 kinase rendered intrinsically resistant to inhibition by rapamycin in situ are not able to protect coexpressed eIF-4E BP1 from rapamycin-induced dephosphorylation. We conclude that mTOR is an upstream regulator of eIF-4E BP1 as well as the p70 S6 kinase; moreover, these two mTOR targets are regulated in a parallel rather than sequential manner.

Animals↗
PubMed1997

Development of flexible ventriculoscope (Yamadori-type VII) and its application to experimental animals.

We developed a new ventriculoscope (Yamadori-type VII), a 2.1 mm calibrated fiberscope with a monopolar coagulator, that can be inserted from the cisterna cerebellomedullaris into the third cerebral ventricle of experimental animals, like dogs. With the improved performance of the neuroendoscope compared to its prototype, Yamadori III, it was possible to inspect clearly and to produce electrocoagulative lesions accurately on any part of the intraventricular structures with minimal injury to nearby vital brain areas.

Animals↗
PubMed1997

Activation of translation initiation factor eIF2B by insulin requires phosphatidyl inositol 3-kinase.

Eukaryotic initiation factor eIF2B mediates a key regulatory step in peptide-chain initiation and is acutely activated by insulin, although, it is not clear how. Inhibitors of phosphatidylinositide 3-kinase blocked activation of eIF2B, although rapamycin, which inhibits the p70 S6 kinase pathway, did not. Furthermore, a dominant negative mutant of PI 3-kinase also prevented activation of eIF2B, while a Sos-mutant, which blocks MAP kinase activation, did not. The data demonstrate that a pathway distinct from MAP and p70 S6 kinases regulates eIF2B. Glycogen synthase kinase-3 (GSK-3) phosphorylates and inactivates eIF2B. In all cases, eIF2B and GSK-3 were regulated reciprocally. Dominant negative PI 3-kinase abolished the insulin-induced inhibition of GSK-3. These data strongly support the hypothesis that insulin activates eIF2B through a signalling pathway involving PI 3-kinase and inhibition of GSK-3.

Androstadienes↗
PubMed1997

Inhibition of the binding of SNAP-23 to syntaxin 4 by Munc18c.

SNARE proteins have been implicated in the insulin-induced translocation of vesicles containing the GLUT4 glucose transporter to the plasma membrane of adipocytes. The role of the target SNARE SNAP-25 or its homologs in this process was investigated by screening a mouse adipocyte cDNA library with rat SNAP-25 and human SNAP-23 cDNA probes. Both positive clones isolated encoded a protein with 87% sequence identity to human SNAP-23, and which was therefore designated mouse SNAP-23. Immunoblot and immunofluorescence analyses revealed that SNAP-23 is located predominantly in the plasma membrane of 3T3-L1 adipocytes incubated in the absence or presence of insulin. Of syntaxins 1 to 5, SNAP-23 bound with the highest affinity to syntaxins 1 and 4 in the yeast two-hybrid system. Expression of SNAP-23, syntaxin 4, and the syntaxin-binding protein Munc 18c in COS cells revealed that Munc18c reduced the amount of SNAP-23 bound to syntaxin 4 in a concentration-dependent manner. These results suggest that the binding of SNAP-23 to syntaxin 4 is inhibited by Munc18c in adipocytes.

Adipocytes↗